One of the larger magnetic fields a relic neutrino encounters
en route to local detectors is that of our galaxy, \(B_g \sim 10\mu \) G.
Galactic fields do not point in a uniform direction, but rather
their orientation changes over a coherence length, \(\Lambda _g\) , of order
kpc [1]}, [2]}, [3]}, [4]}. The spin orientation undergoes a random walk
through the changing directions of magnetic field, reducing
the net rotation by a factor \(\sim \sqrt{\ell _g/\Lambda _g}\) , where \(\ell _g\) 
is the mean crossing distance of the galaxy, of order the galactic
volume \(V_g\)  divided by \(\sigma _g\) , its cross-sectional area. Thus the
square of the spin rotation of a neutrino passing through a given
galaxy (\(g\) ) is
\(\langle \theta ^2\rangle _{g} \simeq \left(2\mu _\nu B_g\frac{\Lambda _g}{v}\right)^2 \frac{\ell _g}{\Lambda _g}\) 
